Kikuyu vs Couch vs Buffalo vs Zoysia: which lawn drinks the most?

In LawnSuite's model, Buffalo has the highest base crop coefficient, Kikuyu the lowest, and Couch and Zoysia sit between them. That's a comparison of the values LawnSuite uses, not proof that every Buffalo lawn drinks more than every Kikuyu lawn. How often you need the sprinkler also depends on how much useful water the roots can reach.

I grow Sir Walter Buffalo on heavy clay in Ipswich, and I haven't run a backyard trial of all these grasses. What I can show you is the water-balance logic I built into LawnSuite, where the assumptions come in, and why a grass name alone isn't enough to set a watering day.

The values LawnSuite uses

These are the base settings in LawnSuite's App source, checked on 23 September 2026. They're software modelling choices, not measurements of your lawn and not a species table published by FAO.

Kc adjusts the weather demand. Reference evapotranspiration, ET0, estimates water loss from a defined reference surface using weather inputs. Multiplying it by a crop coefficient estimates the lawn's evapotranspiration. In the same weather, a larger coefficient gives a larger estimated draw on soil water. LawnSuite also adjusts these base coefficients for season; they aren't fixed year-round daily demand values.

Effective root depth describes the model's accessible soil layer. It isn't a claim that every Couch root stops at the number in the table, or that every Buffalo lawn reaches its assumed depth. Compaction, the soil profile and lawn condition can change the roots you actually have.

The irrigation-depth column is a separate app setting. It is not a weekly requirement, the soil's storage capacity, or an instruction to apply that amount whenever you water. The default row is the source's fallback where it doesn't resolve a supported genus; it isn't another grass species or evidence that all other grasses behave alike.

What FAO-56 actually supplies

The edition consulted here is FAO Irrigation and Drainage Paper 56 Rev.1, second edition, revised 2025. Its Table 6.4, printed page 176 has one general lawn row, rather than separate Buffalo, Couch, Kikuyu and Zoysia rows. It also has separate golf-course and urban-turf rows, so “one turf row in the whole table” would be misleading. A public university-hosted copy of the revised paper is available too.

FAO supplies a method for estimating demand and accounting for soil water. It doesn't certify the per-genus settings above. Keeping those things separate matters: calling something “FAO-56” doesn't turn every assumption built around it into an FAO recommendation.

Why roots can matter more than Kc for the watering interval

Think of Kc as helping estimate how quickly water leaves, and the root zone as the store the lawn draws from. A smaller store can need replenishing sooner even when daily use is fairly modest.

Take Couch and Zoysia in the table. Their base Kc is the same, but the assumed Couch root zone is deeper. With identical soil water-holding capacity, 200 mm of accessible soil holds one-third more available water than 150 mm. If each profile is replenished and you allow the same fraction to be depleted, the deeper one can support a longer dry-weather interval. That's a controlled illustration, not an app-generated schedule.

For comparison, moving from Kc 0.60 to 0.70 increases estimated demand by about 17% in otherwise identical conditions. Across these selected settings, the rooting-depth difference changes potential storage more than the coefficient spread changes demand. That's why I'd check the root zone before arguing over a small Kc difference.

The qualification matters. Deeper roots only help if there's usable water in the deeper soil. A compacted Couch lawn with shallow roots might not have the assumed storage at all. A bigger store also doesn't make ongoing evaporation and transpiration disappear: it changes how long the lawn can go between refills, not necessarily its total water use.

The revised FAO paper's soil-water balance relates available storage to soil properties and root depth, and distinguishes total storage from the portion that can be used before stress. NC State's turf-water explanation also shows why roots, soil, rainfall and irrigation coverage belong in the timing decision. Its US watering figures aren't a schedule for an Australian backyard.

So which should you water more?

I wouldn't set a timer from the ranking alone. Check where the roots are growing, whether the soil down there is drying, how much rain actually soaked in, and whether the sprinkler reaches the whole area evenly. Water running onto the path isn't filling the root zone, and a damp surface isn't proof that the deeper profile is replenished, either.

For an established lawn, respond to the actual soil and weather rather than adding water simply because another week has passed. Freshly laid turf and lawns recovering from damage need separate establishment or recovery advice. Local watering restrictions still govern when you can irrigate.

The FAO-56 city-by-city comparison answers the broader climate question. It uses its own declared seasonal assumptions and averages separately calculated yearly balances; it doesn't turn the genus table here into an annual saving or a weekly prescription. For care beyond watering, see the Sir Walter guide and Kikuyu guide.

If you don't yet know how much lawn you're watering, start with the free lawn-size calculator. Measure the turf rather than the whole block, then keep observations of the lawn alongside the model's estimate.

About Macca: I built LawnSuite and its FAO-56 water-balance engine. My own lawn is Sir Walter on heavy clay in Ipswich; this comparison explains the model rather than claiming personal trials of every grass.